LizEF is right on about the Eco and 3776. Platinum says the 3776 Century pens can sit for two years withour drying out. That start at $150 in the US.
Here is some more information for you.
Drying out when a pen is not in use is primarily a function of how well the pen's cap seals. Inks do vary in this respect, but that is more secondary. As to clogging, any ink dried in the feed will stop flow. Permanent inks are not necessarily more prone to clogging than non-permanent inks.
If a nib has dried out it is usually easy to get it started again. I often just rinse the nib in tap water, then wipe it off with a paper towel and the ink starts flowing again. If it is really stubborn and you can remove the grip section from the pen, take out the cartridge or converter, you can flush the feed and nib with tap water using a bulb syringe. Then reassemble the pen.
I have used Noodler's Black for many years, and in my Vanishing Point the pen was not hard starting after two weeks of non use. This ink and other's designated "bulletproof" by Noodler's contains a dye that chemically bonds with the cellulose fibers in paper within a few hours after drying. These inks cannot be removed with solvents, soaps, water, bleach, nor any known method without destroying the paper. I find they are not difficult to clean out of my pens. By the way, Noodler's Black is Goulet Pens top selling ink of the 600 inks they sell. It is one of the best on low quality paper and very resistant to feathering and bleeding through cheap paper. For me it has been a wonderfully behaved ink in many of my 40+ pens, and I have never used it in a pen where it did not perform perfectly (except when the pen had a problem).
The $4 Platinum Preppy pen can go for months capped with no use without drying out. Preppy pens are not that rugged, though are very nice writing pens.
It uses Platinum cartridges, but I use an ink syringe to fill the cartridges with bottled ink. Platinum has a pigmented carbon ink that is waterproof and is available in cartridges for all Platinum cartridge pens.
A TWSBI Eco will seal so the pen can set for months without drying out. It is a piston filling pen that holds a lot of ink, has an inner cap that seals the nib and the cap seals to the barrel with an O-ring making it doubly air tight ($29).
The Platinum Balance and Cool pens seal very well ($38). Balance pens are opaque, the Cool pens are transparent.
The Platinum Plaisir ($18) uses the Preppy nib/feed/grip section but is armored with an aluminum barrel and cap so it is a ruggedized Preppy. It seals just like the Preppy with an inner cap that can sit for months without drying out.
You don't say what pens you have now. The vast majority of inks are not permanent. Historically there are inks that are labeled "Washable" and "Permanent" that DO NOT RELATE TO HOW THEY BEHAVE ON PAPER. Sheaffer inks so labeled in the past meant that the ink was washable or permanent when it got on clothing. I don't know if these terms are used today, but most inks today that are labeled "permanent" means they are waterproof. I have used a black ink that was labeled "Permanent" back in the late 90's that was washed away with water. I think it was Parker Quink, but may have been Sheaffer ink, I can't remember.
Hope this helps you.
Edited by graystranger, 10 March 2018 - 15:58.